BEC/Fraud: Urgent language and suspicious sending/infrastructure patterns

name: "BEC/Fraud: Urgent language and suspicious sending/infrastructure patterns"
description: "Identifies inbound messages using urgent language patterns and sender behavioral traits common in social manipulation. Combines multiple indicators including urgent subject lines, characteristic message content, short message length, and suspicious sender attributes."
type: "rule"
severity: "medium"
source: |
  type.inbound
  and 3 of (
    // urgent subjects
    strings.ilike(subject.subject, '*quick question*'),
    strings.ilike(subject.subject, '*urgent*request*'),
    strings.ilike(subject.subject, '*are you available*'),
    strings.ilike(subject.subject, '*need assistance*'),
    strings.ilike(subject.subject, '*help*needed*'),
    regex.icontains(subject.subject, 'favor\b'),
    strings.ilike(subject.subject, '*checking in*'),
    strings.ilike(subject.subject, '*awaiting*response*'),
    strings.ilike(subject.subject, '*catch*up*'),
  
    // BEC body patterns
    strings.ilike(body.current_thread.text, '*sorry to bother*'),
    strings.ilike(body.current_thread.text, '*are you busy*'),
    strings.ilike(body.current_thread.text, '*can you help*'),
    strings.ilike(body.current_thread.text, '*do you have a moment*'),
    strings.ilike(body.current_thread.text, '*please respond*asap*'),
    strings.ilike(subject.subject, '*quick question*'),
  
    // brand name
    regex.icontains(body.current_thread.text, 'a\s?m\s?a\s?z\s?o\s?n'), // Catches "Amaz on", "Amazon", etc.
    regex.icontains(body.current_thread.text, 'p\s?a\s?y\s?p\s?a\s?l'),
    regex.icontains(body.current_thread.text, 'a\s?p\s?p\s?l\s?e'),
  
    // short body
    length(body.current_thread.text) < 200,
    strings.count(body.current_thread.text, ' ') < 30
  )
  and 3 of (
    // suspicious sender
    sender.email.domain.root_domain in $free_email_providers,
    network.whois(sender.email.domain).days_old < 30,
  
    // suspicious recipient pattern
    any(recipients.to, strings.ilike(.display_name, 'undisclosed?recipients')),
    length(recipients.to) == 1, // Single recipient
  
    // header checks
    strings.starts_with(headers.mailer, 'Open-Xchange Mailer'),
    strings.ilike(headers.x_originating_ip.ip, '*.*.*.0'), // Common in some BEC campaigns
    // deifferent reply-to address
    (
      length(headers.reply_to) > 0
      and sender.email.email not in map(headers.reply_to, .email.email)
    ),
    // sender display name is part of the subject
    strings.icontains(subject.subject, sender.display_name),
  )
  and profile.by_sender_email().prevalence not in ("common")
attack_types:
  - "BEC/Fraud"
  - "Callback Phishing"
  - "Spam"
tactics_and_techniques:
  - "Impersonation: Brand"
  - "Social engineering"
  - "Free email provider"
detection_methods:
  - "Content analysis"
  - "Header analysis"
  - "Sender analysis"
  - "Whois"
id: "ba8a79e0-cce3-57e8-bbc7-3b3d9f848761"